Martens’ lack of shyness helped him become a successful dealer of concert merchandise in the 1990s, which in turn helped him become friendly with famous musicians. That is how Martens is able to throw himself one doozy of a 50th birthday party in Portland this weekend, with John Popper of Blues Traveler and Chris Barron of Spin Doctors playing live as part of the entertainment.

Martens is calling the event the F.O.G. (Friends of Greg) Festival, with shows at The Big Easy on Thursday and Friday, and at Port City Music Hall on Friday and Saturday.

It’s not a private party, either — anyone can buy a ticket to the shows and join the fun.

Not only are Popper or Barron — or both — playing at each show, the concerts feature a ton of local musicians as well, including The Fogcutters big band, The John Clavette Band, DIRIGO, Anna and The Diggs, The Blues Brothers Tribute Band featuring Martens, and even some comedy by Birdie Googins, aka “The Marden’s Lady” of local TV commercials.

But the F.O.G. Festival is not just about Martens getting all his friends together to help him blow out his candles. Martens is a self-styled entrepreneur who can’t sit still, and since he turned 40, he’s been periodically throwing himself birthday party/rock concerts that also serve as fundraisers for local charities.

The beneficiary this year and for the past several years has been Good Shepherd Food Bank in Auburn, which receives a percentage of the ticket sales. Money will be raised by donations and raffles as well.

“I need to keep busy, and I want to do something that might have a positive effect,” said Martens, who will turn 50 on Sunday. “But the big reason I do this is to get all my friends together, old friends and new friends. When I was on the road (selling concert merchandise), I met a lot of people, but they’re scattered all over the place.”

To be clear, Martens is paying to have Popper and Barron play. They’re not working for free just because they know and like him.

But if Martens didn’t know them personally, it’s hard to see them doing four shows with dozens of local musicians. Both Popper and Barron say they truly wanted to be part of F.O.G. Fest after hearing so much about the events over the years.

Popper is performing “because I am a F.O.G. — friend of Greg’s — and I think what he is doing is really important, giving back to the community,” he said via email. “Over the years, we have tried to make this happen, but I was always booked with Blues Traveler, so I was happy that it worked out this time.”

Popper, who will also sing the National Anthem before the Portland Red Claws game on Friday, said Martens was the first T-shirt and merchandise seller Blues Traveler had at its concerts, and that he “did it better than anyone, I must say.”

Martens even lived with Blues Traveler members in the band’s Brooklyn, N.Y., apartment for a while. And because the Spin Doctors were close buddies with Blues Traveler, it made sense that Martens would get to know that band as well, said Barron.

Martens grew up in Camden, where his father worked in furniture restoration. While in college at Boston University, he helped set up a show for Frank Zappa and got a taste of the concert business.

He was also a Deadhead, and he parlayed following the Grateful Dead around the country into a job selling T-shirts at their concerts from 1987 to 1992. So it should come as no surprise that Marten got former Dead keyboardist Tom Constanten to perform at F.O.G. Fest last year.

Martens began working at Blue Traveler shows in 1992 and became the tour merchandise supervisor. He did that for a few years before returning to Maine and starting or working in various businesses.

But all the time, he’s kept in touch with his musician friends. He even performs himself around Maine, as Jake Blues in The Blues Brothers Tribute Band.

Because this year is his 50th birthday, Martens wanted to make his F.O.G. Fest bigger than it’s ever been. Thus the four shows and two major rock stars.

Blues Traveler, with Popper as frontman, helped create the jam-band scene of the 1990s (including the HORDE Festival), and scored a number of radio hits such as “But Anyway,” “Run-Around” and “Hook.”

A series of events — including Popper’s battle with obesity and the 1999 death by accidental drug overdose of bassist Bobby Sheehan — helped end the band’s days as a powerhouse act. But it’s still recording and touring, and its latest studio album, 2012’s “Suzie Cracks the Whip,” was the band’s first to crack the Billboard 100 since 2001.

Spin Doctors had a similar progression, gaining fame in the 1990s with a stripped down yet poppy rock sound, most notably on the hit singles “Little Miss Can’t Be Wrong” and “Two Princes.” The band released a new studio album, “If the River Was Whiskey,” in early February.

As luck would have it, Martens put together his 50th birthday party with Popper and Barron, then broke his ankle slipping on some steps in February.

But here’s where his lack of shyness helps again.

“It just means I’ll be at the shows wheeling around in a wheelchair. I’ll still do the John Belushi part (in the Blues Brothers tribute band),” said Martens. “Maybe I can do a couple backflips in a wheelchair.”

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